The present invention generally pertains to an electronic control system for controlling two electric motors, and more particularly pertains to an electronic control system for controlling two separately excited electric motors of a vehicle in such a manner as to provide automatic traction control.
The use of electric motors to propel vehicles has become increasingly more common. Electric motors have been used on trains for decades and are now used on electric and hybrid-electric automobiles and trucks. Unlike vehicles that solely rely on combustion engines, vehicles that use electric motors may employ an electric motor for each drive wheel. FIG. 1 shows an example of a control system for controlling two separately excited electric motors 12a and 12b used to drive two drive wheels on opposite sides of the vehicle. As shown, each motor 12a and 12b includes a respective armature 15a and 15b and field component 17a and 17b. Each motor 12a and 12b is part of a respective drive system 20a and 20b provided for the right and left wheels at the front or rear of the vehicle.
Each drive system 20a and 20b includes its own microprocessor 25a and 25b coupled to a respective power interface 30a and 30b. Each system 20a and 20b further includes a main power switch 35a and 35b coupled in series with respective armatures 15a and 15b, while having a control terminal coupled to power interface 30a and 30b, respectively. Main power switches 35a and 35b are used to control the speed of motors 12a and 12b in response to signals originating from microprocessor 25a and 25b. 
Drive systems 20a and 20b each include a respective bypass switch 37a and 37b coupled across armatures 15a and 15b so as to selectively divert current from armatures 15a and 15b in response to control signals originating from microprocessors 25a and 25b. In addition, each drive system 20a and 20b includes a first low power switch 41a and 41b, a second low power switch 42a and 42b, a third low power switch 43a and 43b, and a fourth low power switch 44a and 44b. These low power switches are coupled to opposite ends of field components 17a and 17b and operate under control of microprocessors 25a and 25b to change the polarity of the power supplied to field components 17a and 17b so as to rotate the motors and hence the wheels forward or reverse.
The two drive systems 20a and 20b generally operate separately and the motors 12a and 12b are separately excited. A steering potentiometer 50 may be provided that is coupled to the vehicle's steering wheel so as to signal the microprocessors 25a and 25b that the vehicle is turning and to what extent. Microprocessors 25a and 25b also receive a signal representing the vehicle speed. Microprocessors 25a and 25b respond to these signals by independently and selectively varying the speed of the motors 12a and 12b using main power switches 35a and 35b. Thus, when a vehicle is turning, the microprocessor of the drive system driving the inside wheel causes its motor to operate at a lower speed, while the microprocessor of the drive system driving the outside wheel causes its motor to operate at a higher speed.
The system shown in FIG. 1 does not provide any form of traction control or differential lock. Another drawback to the system of FIG. 1 is that it utilizes two separate electronic control units, which together employ two microprocessors, four high power switches and eight low power switches.
Traction control utilizing a single electronic control unit has been available for many years concerning the control of two series-wound DC electric motor systems. An example of such a system is shown in FIG. 2.
FIG. 2 shows a drive system including a single electronic control unit and two motors with armatures 115a and 115b connected in parallel, effectively acting like an electronic differential, similar to the mechanical differential on a car. When one of the wheels spins, as detected via a speed sensor on each wheel, a microprocessor 125 changes the wiring of the armatures 115a and 115b of the two motors via a power interface 130 and two change-over contactor/relays 114a and 114b, to be connected in parallel, at which time equal power will be applied to the two wheels, allowing the wheel which is still on the ground (as opposed to the spinning wheel) to move the vehicle. As there is no means to know when the microprocessor 125 should change the connection of armatures 115a and 115b to go back to the differential mode, the program will allow the armatures 115a and 115b of the two motors to be connected back in series mode after a time delay. If one of the wheels is still spinning, then armature connection will be changed again, as noted above, to repeat the process again. This process will continue, i.e., the vehicle will stop and then start again until both wheels gain traction.
As further shown in FIG. 2, a main power switch 135 selectively completes the circuit of the vehicle batteries 151 and 152 and armatures 115a and 115b. The field components 117a and 117b of the two motors are also connected in series with the batteries and the armatures. The polarity of the field components may be switched via relay switches 141 and 142. A circuit breaker 155 may be coupled in series with armatures 115a and 115b. In addition, an operator interface 150 may be coupled to microprocessor 125 so as to provide vehicle speed and turning information.
Although the system shown in FIG. 2 provides a form of traction control, the two motors are not separately excited, which gives only limited control.
It has not previously been known to use ea single electronic control unit device which can bring about automatic traction control in two or more separately excited motor systems.